Acute exacerbations are an important contributor to the health care costs, quality of life, morbidity, and mortality of patients with chronic obstructive pulmonary disease (COPD). Airway bacterial infection may promote increased airway inflammation and lead to decreased airway function, and nontypable Haemophilus influenzae is the bacterial species most commonly isolated during COPD exacerbations. H. influenzae strains isolated from COPD patients during acute exacerbations induce more inflammation in a mouse airway infection, induce higher levels of interleukin-8 after interaction with human airway epithelial cells, and adhere more to epithelial cells compared to colonizing strains. Based on these observations, we hypothesize that specific H. influenzae surface molecules control airway epithelial cell interactions with bacteria that determine bacterial capacity to induce high levels of airway inflammation and COPD exacerbations. A better understanding of interactions between H. influenzae and epithelial cells that lead to airway inflammation may uncover strategies for selectively modifying damaging bacterial effects but not beneficial immunity in airway epithelium in patients with COPD. Accordingly, our specific aims are to: I. Compare the airway epithelial cell response to H. influenzae associated with COPD exacerbation versus colonization. We propose that H. influenzae associated with COPD exacerbations induce more inflammation compared to colonizing strains. To investigate this aim, we will take advantage of airway epithelial cell models (including primary cultures of human tracheobronchial epithelial cells) and their sensitivity to interaction with H. influenzae. Comparison of bacterial strains will be accomplished using assays of bacterial adherence and epithelial cell signal transduction pathways and gene expression. II. Determine epithelial cell mechanisms that detect and respond to H. influenzae associated with COPD exacerbations. We propose that specific molecules on the epithelial cell surface detect H. influenzae and activate specific signaling pathways leading to gene expression. To investigate this aim, we will take advantage of the same airway epithelial cell model systems for H. influenzae infection and epithelial cell responses. Critical molecules and pathways important in airway defense will be determined by detecting activation and using specific inhibitory strategies such as dominant-negative molecule expression. III. Identify bacterial factors that regulate the airway epithelial cell response to H. influenzae associated with COPD exacerbations. We propose that specific bacterial molecules interact with and/or are detected by epithelial cells, and that these molecules differ between strains of H. influenzae associated with exacerbation versus colonization. To investigate this aim, we will take advantage of multiple systems that differentiate the expression and function of specific bacterial virulence factors. Expression of important bacterial factors will be identified and linked to epithelial cell adherence and responses.